This invention relates to means for automatically restricting the flow of fluid in conduits leading to and/or from fluid actuated cylinder means for causing pivotal movement of a member whereby the speed of pivotal movement of the member is rapid during one portion of its pivotal movement but is automatically reduced during a predetermined portion of its subsequent pivotal movement, thereby minimizing failures of the components of the member which is being moved and of the fluid system and improving the braking action for reducing the speed of pivotal movement of the member.
Many devices have members which are pivotally moved by fluid actuated cylinder means, for example the pivotal movement of the turret carrying the boom and bucket of a backhoe, trencher or other excavating device. A need has long been recognized to provide means for automatically slowing down or braking the pivotal movement of such a member near the end of its pivotal movement in order to prevent damage to the apparatus when at the end of its pivotal movement the movement is completely stopped.
In my prior U.S. Pat. No. 3,407,946, dated Oct. 29, 1968, I disclosed a pair of fluid operated cylinder means and a pair of throttling valves. Each throttling valve was operable by a spring and a cam on the turret of a backhoe and followers to restrict the flow of fluid in the conduit which led from the end of one fluid cylinder means to the main control valve during the return or inactive stroke of the piston. Because the rod of one fluid cylinder was attached to the turret, a braking effect on the pivotal movement of the turret resulted and that braking effect opposed the pivoting force which was simultaneously being exerted on the turret by the piston of the other fluid actuated cylinder means. However, because during the braking action when the operator continued to hold the main control valve in a position to supply fluid under full volume to the operative end of the fluid actuated cylinder which was exerting the pivoting force and also because the momentum of the loaded bucket and swinging boom was great, it was found in practice that these combined forces during the braking portion of the pivotal movement were of such magnitude that premature and excessive failures of various components of the backhoes resulted.
In my prior U.S. Pat. No. 3,530,766 dated Sept. 29, 1970, I disclosed an improvement upon my above mentioned prior patent. This patent also used a pair of fluid operated cylinder means and a pair of throttling valves. Each throttling valve was operable by a spring and a cam on the turret of the backhoe and followers to restrict the flow of the fluid in the conduit which led from the source of fluid under pressure to the operative end of the cylinder which was exerting the pivoting force on the turret. However, it has been found in practice that the correct timing of the cams and followers of the apparatus of this patent is very difficult to achieve, that inertia or momentum of the boom during the braking action continues to counteract the effectiveness of the braking action and that the cost of manufacturing and assembling the cams, followers, throttling valves and associated parts is very expensive.
Consequently the apparatus of my two above identified U.S. patents have not solved the above mentioned long-felt need and it has not been solved by any other prior apparatus of which I am aware